Implantable medical devices have been developed to provide ongoing monitoring of the physiological state of a patient and, when indicated, automatically provide therapy for detected conditions. One particular type of implantable medical device is a pacemaker which can be combined with an implantable cardioverter-defibrillator (ICD) which can automatically monitor the patient's cardiac activity and provide therapeutic pacing stimulation for bradycardia and tachycardia conditions as well as a defibrillating shock upon detection of a fibrillation condition. Such implantable devices typically comprise a microprocessor-based controller, a pulse generation circuit operating under control of the microprocessor, and one or more sensing and stimulation electrodes which are typically implanted in contact with the patient's cardiac tissue and are connected to the implantable device via one or more leads. The devices are also typically capable of self-monitoring by detecting a variety of conditions of the implantable device itself.
There are times when it is desirable to alert the patient of certain conditions which the device may detect, such as detection of a change in device operation or detection of certain physiological conditions. Examples of such situations include: a change in capture threshold, failure of a lead or other component of the device, and an increase in the number of pacemaker-mediated tachycardia (PMT) responses indicating possibly inappropriate programming. These conditions may not be noticeable to the patient yet may still indicate that further intervention or reprogramming of the implanted device would be warranted. For example, the patient may need to arrange a visit with an attending clinician to reprogram/repair/service the device or to modify or begin a medication regimen.
In the particular example of implantable defibrillators, as delivery of therapy can be physically and psychologically traumatic to the patient, it is sometimes deemed preferable to alert the patient to the prospect of the eminent delivery of therapy. One example of the desirability of this is that, in the case of ventricular tachycardia/ventricular fibrillation (VT/VF) patients, detection of such a tachycardia condition may precede a syncopal episode. In such a case, the patient could be alerted/advised to sit, recline, or take other action to avoid potential injury, such as pull to the side of the road if driving.
In the particular case of atrial tachycardia/fibrillation (AT/AF) patients, some of these AF patients do not consciously notice when they enter into an AF episode. Therefore, they are not aware of the condition or that they could benefit from treatment, such as administration of medication. According to published literature, up to one third of patients with clinically recognized AF have what is known as silent AF, e.g. they are unaware of ongoing AF episodes at least part of the time. Further, Holter and transtelephonic monitoring also indicates that for patients with paroxysmal AF (PAF), at least ninety percent of AF episodes are asymptomatic.
It has long been recognized that episodes of AF tend to contribute to further ongoing episodes of AF. Atrial fibrillation and atrial flutter are also known to increase the risk of thromboembolism. Thus, many physicians believe it is best to maintain sinus rhythm as much as possible in patients with episodes of persistent AF via, for example, administration of electrical and/or pharmacological cardioversion. Anticoagulation medication is also a standard therapy for chronic AF and PAF patients, particularly before and after pharmacological or electrical cardioversion. Accordingly, these patients would benefit from a system to make them consciously aware of their arrhythmia so that they may seek appropriate treatment, e.g. administration of anticoagulation medication and/or electrical or pharmacological cardioversion.
Implantable medical devices, such as implantable cardiac stimulators, are known which provide alerts or other warning signals to notify the patient of certain conditions. However, several shortcomings exist in the prior art, especially as would relate to alerting patients of silent AF. These shortcomings include the requirement for special dedicated electrodes for providing notification in addition to electrodes otherwise required by the implantable device which add to the cost and complicate the implant procedure. Also, conditions indicating a notification may occur at a time at which the patient is not in a condition to readily notice such a notification, such as during sleep or strenuous physical activity and notifications provided at the time of occurrence may go unnoticed. Further, a notification may be noticed but, as no input is provided to the device if appropriate corrective action has been taken, it remains indeterminate whether subsequent reminder notifications are indicated or not.
Thus, it will appreciated that there is an ongoing need for an implantable medical device which can effectively provide notification to a patient upon detection of conditions indicating notification, such as detection of a silent AF or a change in device operation or condition. There is a need for an implantable medical device with notification features that avoids the need for special or separate structures, such as a notification electrode. There is a need for an implantable medical device which can notify the patient in a manner and at a time selected to increase the likelihood that the patient will notice the notification. There is also a need for an implantable medical device that can monitor for corrective action taken and provide subsequent follow-up notifications as indicated. There is also a need for an implantable medical device where the patient can delay notifications when desired. There is also a need for an implantable medical device which can provide notification in the presence of R-waves and premature ventricular complexes (PVCs).